Vehicle restraint deployment controls are increasing in ability to classify vehicle seat occupants on the basis of sensed occupant characteristics such as weight and determine and/or adjust deployment on the basis of such classification. To accurately determine vehicle seat occupant weight, such systems may compensate a vehicle seat occupant weight signal, derived from a suitable occupant weight sensor, in response to a belt tension sensor, in order to remove inaccuracies caused by the downward force of a tightly cinched seat belt on the seat occupant. But such compensation may itself be inaccurate if the seat belt is pinched or snagged between the tension sensor and the occupant so that the belt tension sensor signal from the belt tension sensor does not represent the true downward force of the belt on the occupant.
For example, referring to FIG. 1, a prior art vehicle seat apparatus 10 comprises a seat frame 12 and a seat cushion 14. A pressure sensor 16 is disposed to sense the pressure of a mass 18 such as an occupant or an object on seat cushion 14, the sensor being located, for example, between seat cushion 14 and seat frame 12. Seat 10 is provided with a seat belt apparatus comprising a flexible restraining belt generally indicated as 20 and extending between a latch side anchor 30 and an opposite side anchor 32. A first section 22 of belt 20 extends between anchor 30 and a latch portion 25. The remainder of belt 20 is a single, separate piece with three continuous sections: (1) section 28 between latch portion 24 and a retractor 38 typically anchored on the “B” pillar of the vehicle on the opposite side (outside) from the latch, (2) section 27 between latch portion 24 and an object 34 pinching or kinking the belt, and (3) section 26 between object 34 and anchor 32. During the operation of this invention latch portions 24 and 25 will be latched together into a single latch 24, 25. In many applications, the belt is slidable through latch portion 24; and the relative lengths of sections 27 and 28 will change as the belt so slides. Alternatively, each of sections 27 and 28 may be separately attached to latch portion 24. At the end of belt 20 opposite latch 24, 25, a belt tension sensor 36 is disposed between the end of belt 20 and anchor 32. Anchors 30 and 32 are firmly attached to the vehicle body to restrain mass 18 against seat cushion 14 in a vehicle crash as is well known in the art.
Latch 24, 25 allows unfastening of the two separable parts—22 and 26, 27, 28—of belt 20 for occupant ingress and egress; but while latch 24, 25 is latched, belt 20 is capable of maintaining a sustained tension force having a downward component on restrained mass 18 and thus distorting the pressure sensed by pressure sensor 16. Belt tension sensor 36 provides a signal of belt tension force to a control also receiving an occupant weight signal from pressure sensor 16 so that the occupant weight signal may be compensated by the belt tension to more accurately and dependably estimate the weight of occupant (restrained mass) 18 on seat cushion 14. The estimated weight is used to characterize the occupant of the seat in order to control the deployment of an airbag or similar passive restraint during a vehicle crash event. But belt tension sensor 36 itself can be fooled by an object 34 that pinches or kinks belt 20 and thus changes the tension on the side of the belt—section 26 in this example—adjacent the belt tension sensor. For example, in the apparatus as shown, belt tension sensor 36 provides a signal of the tension in section 26 of the belt, between anchor 32 and object 34, that may not be the same as the tension in section 27 of the belt adjacent restrained mass 18, due to the interference of object 34.
A similar prior art apparatus is shown in FIG. 2, with similar elements having identical reference numerals. The differences are: (1) belt tension sensor 36 is on the opposite side of seat cushion 14, between anchor 30 and belt section 22; (2) object 34 is also on the opposite side of seat cushion 14, although it is on the same side of latch portion 24 and is interfering with section 27, 28 of belt 20; and (3) the proportion of section 27 to section 28 of belt 20 in this example is different from that of section 27 to section 28 of the belt of FIG. 1, due to the different location of object 34. The same problem occurs with respect to object 34, which prevents belt tension sensor 36 from accurately sensing the tension force in belt 20 that affects the output of pressure sensor 16; and this problem would also be present if object 34 were interfering with section 22 of the belt. The problem is the same, but the side is different.